1. Field of the Invention
The present invention relates to a film forming condition determination method capable of controlling the state of generation of an accompanying dielectric film that is generated with the formation of high-dielectric constant film or ferroelectric film, and efficiently determining an optimal film forming condition, for making the film structure closer to an intended film structure, relates to a film forming method capable of shifting smoothly a prototype of film structure to a mass-production stage, and further relates to a film structure manufacturing method capable of realizing an improvement in the yield, when mass-producing the film structure.
2. Description of Related Art
Conventionally, there are products produced using a film structure obtained by forming a high-dielectric constant thin film or ferroelectric thin film on a substrate, such as various kinds of semiconductor memory and semiconductor devices, and specific examples of these products include DRAM (Dynamic Random Access Memory), FRAM (Ferroelectric RAM), capacitor, piezoelectric elements such as an actuator, and electro-optic elements such as an optical shutter and an optical isolator.
For the film structure for use as a material for the above-mentioned various kinds of semiconductor products, first, the operation of finding a plurality of variables (parameters) concerning a film forming condition for manufacturing an intended film structure is performed, and then a prototype of the film structure is manufactured, based on the parameter values considered optimal. In order to examine whether the prototype has intended characteristics, in general, the prototype's evaluation is based on electrical measurement.
In order to electrically evaluate the prototype, first, an electrode part is formed on the prototype, then a required voltage is applied, by bringing a conducting probe into a contact with the formed electrode part (probing), or by wire bonding, and finally the capacitance (electric capacitance) of the dielectric film is measured to evaluate whether the prototype has intended characteristics. However, in order to evaluate the relationship between the film thickness and the dielectric constant from the measured capacitance, it is necessary to form, measure and compare a plurality of prototypes with different thickness. Note that the frequency band for electrical measurement of the dielectric constant ranges from about 100 kHz to about 5 GHz.
After confirming that a prototype has the intended characteristics, through the above-mentioned measurement and evaluation, products equal to the prototype should be manufactured in a factory, by a film forming apparatus, due to the shift from the prototype to a mass-production stage.
However, since a film forming apparatus for manufacturing the prototype and a film forming apparatus for mass-production in the factory differ in the scale, etc., even if the film forming conditions, optimized for the film forming apparatus for prototype are applied, as it is, to the film forming apparatus in the factory, products having the same characteristics as the prototype are rarely obtained. Therefore, a mass-production prototype is manufactured, by adjusting the film forming condition of the film forming apparatus in the factory, and then electrical measurement and evaluation of the manufactured mass-production prototype are done in the same manner as in the prototype stage, and the determination process of the optimal film forming conditions, for manufacturing a mass-production prototype having the same characteristics as the prototype, is performed.
After determining the optimal film forming conditions, those conditions are set for the film forming apparatus in the factory, and manufacture (mass-production) of film structure is performed. The manufacture of film structure includes a plurality of film forming steps, and the film structure is completed by performing the processing of the respective steps one after another. Moreover, electrical measurement is performed on the completed film structure as a part of a finished product inspection. It has been known that a transmission electron microscope (TEM) or a spectroscopic ellipsometer are used for the measurement of the film structure, as well as the above-mentioned electrical measurement.
The analysis performed using the spectroscopic ellipsometer is disclosed in Japanese Patent Applications Laid-Open No. 2002-289614 and No. 2001-126324. The Japanese Patent Application Laid-Open No. 2002-289614 discloses measuring the refractive index of a multi-layer film formed on the substrate entirely with a spectroscopic ellipsometer, and applying the measurement to the evaluation of the dielectric film, the temperature calibration and the manufacturing method. The Japanese Patent Application Laid-Open No. 2001-126324 discloses a method in which the variations in the film thickness and optical characteristic are evaluated by ellipsometer measurement in the course of the manufacture of an optical storage medium, and the manufacturing conditions are changed by feeding back the evaluation results to the manufacturing process. Note that the frequency band for the measurement of dielectric constant by the spectroscopic ellipsometer ranges from several hundred THz to about two thousand THz, and thus largely differs from the frequency band for the electrical measurement.
The above-described conventional electrical measurement has the problem that it takes a lot of time and work. In other words, in order to perform the measurement, first a plurality of film structures to be measured are prepared, and then probing or wire bonding is performed, after creating an electrode part for each film structure, and thus a lot of time and work are required. Note that if the electrode part is once formed on the film structure, the electrode part can never be removed, and therefore it is difficult to effectively use the film structure used for the measurement. Moreover, determining an optimal film forming condition, by evaluating a plurality of measurement results, creates a heavy labor burden, and particularly if the number of kinds of parameters concerning the film forming condition of a film structure to be manufactured is large, the same number of electrical measurements and the evaluation process are required for each kind, and consequently the labor burden increases.
Further, when determining an optimal film forming conditions in order to shift to the mass-production stage in the factory, it is also necessary to perform measurements and evaluation. However, since the number of objects to be measured and evaluated at the mass-production stage is much larger compared to the prototype stage, there is the problem that a lot of time and work are necessary to shift to the mass-production stage as well.
Furthermore, after shifting to the mass-production stage, it is physically impossible to form an electrode part after deposition of each intermediate film structure, and perform electrical measurement by probing or wire bonding, therefore, presently, a product inspection is performed on a finished film structure, obtained through a plurality of film forming steps. Thus, since an intermediate film structure, that may contain a defective layer, during any step of a film forming process, flows to the final film forming step, and as a result, a lot of steps are performed wastefully, an improvement of the yield is not achieved.
Since the methods of Japanese Patent Applications Laid-Open No. 2002-289614 and No. 2001-126324 do not take into account the shift to the mass-production stage and an improvement of the yield at the mass-production stage, even if the methods disclosed in Japanese Patent Applications Laid-Open No. 2002-289614 and No. 2001-126324 are applied, the above-mentioned problems cannot be solved. Moreover, the measurement and analysis by a transmission electron microscope (TEM) require even more work, compared with electrical measurement, and the degree of difficulty of the measurement is high. Therefore, even if the transmission electron microscope (TEM) is used, the above-mentioned problem cannot be solved.
On the other hand, in recent years, it was reported that when a high-dielectric constant film or ferroelectric film, whose electrically measured dielectric constant is not lower than 50, is formed on a substrate, an unknown accompanying film having dielectric characteristic is naturally formed following the formation of the high-dielectric constant film or ferroelectric film. This accompanying film may be formed at the interface between the high-dielectric constant film or ferroelectric film and the substrate, on the surface of the high-dielectric constant film or ferroelectric film, or both the interface and the film surface. Moreover, it has been found that when the high-dielectric constant film or ferroelectric film is a multi-layer structure, it may be formed at the interface between the respective films.
Although the presence of such an accompanying film is detected by electrical measurement, the single electrical measurement can not determine the characteristic of the accompanying film and the characteristic of the high-dielectric constant film or ferroelectric film separately. Besides, it is presumable, that the dielectric constant of the accompanying film may become higher or lower compared with the dielectric constant of the high-dielectric constant film or ferroelectric film under some film forming condition. However, it has not yet been established, how the dielectric constant of the accompanying film varies with a change in the film forming conditions, and there is a possibility, that the accompanying film may loose the characteristic of the high-dielectric constant substance or ferroelectric substance, when the dielectric constant of the accompanying film is low. Note that since the refractive index establishes a relationship similar to the dielectric constant, therefore the above discussion is also applied to the refractive index of the accompanying film.
Since the presence of the accompanying film prevents the film structure from having an intended characteristic, it is important to reduce the accompanying film and even more important to find a film forming conditions to eliminate the accompanying film. On the other hand, from a different point of view, it is expected to appreciate the importance of the capability to find a film forming conditions, capable of forming an intended film structure, including an accompanying film, by generating the accompanying film intentionally. However, even when the methods of Japanese Patent Applications Laid-Open No. 2002-289614 and No. 2001-126324 are used, it is impossible to determine a film forming conditions capable of controlling the generation of the accompanying film.